Power quality utility metering system having waveform capture

ABSTRACT

A method of monitoring variations is carried out within an electrical energy meter containing means therein for metering a quantity of electrical energy generated by a supplier and transferred via a power supply line to a load. The method includes a first step of sensing a line voltage transferred via the power supply line to the load during the energy measurement time interval. The method also includes the step of detecting a variation in a magnitude of the sensed line voltage relative to an acceptable voltage level, wherein the variation exceeds a first variation threshold. The method then includes the step of capturing a first waveform of the sensed line voltage corresponding to the time when the variation is detected. Finally, the method includes the steps of detecting a subsequent reduction in the variation of the magnitude of the sensed line voltage such that the variation is equal to or less than the first variation threshold and capturing a second waveform of the sensed line voltage corresponding to the time when the subsequent reduction in the variation is detected.

CROSS REFERENCE TO RELATED APPLICATION

Cross reference is made to U.S. patent application Ser. No. 09/226,957,filed Jan. 8, 1999, which is assigned to the assignee of the presentinvention.

FIELD OF THE INVENTION

This invention relates to electricity meters such as used by commercial,industrial, or residential customers of power utility companies and,more particularly, to a revenue accuracy meter having variousoperational capabilities such as power quality measurement and/or energymanagement.

BACKGROUND OF THE INVENTION

Utility power distribution generally starts with generation of the powerby a power generation facility, i.e., power generator or power plant.The power generator supplies power through step-up subtransmissiontransformers to transmission lines. To reduce power transportationlosses, the step-up transformers increase the voltage and reduce thecurrent. The actual transmission line voltage conventionally depends onthe distance between the subtransmission transformers and the users orcustomers. Distribution substation transformers reduce the voltage fromtransmission line level generally to a range of about 2-35 kilo-volts(“kV”). The primary power distribution system delivers power todistribution transformers that reduce the voltage still further, i.e.,about 120 V to 600 V.

For background purposes, and future reference herein, an example of apower utility distribution system as described above and understood bythose skilled in the art is illustrated in FIGS. 1A and 1B of thedrawings. Power utility companies, and suppliers thereto, have developedsystems to analyze and manage power generated and power to be deliveredto the transmission lines in the primary power distribution system,e.g., primarily through supervisory control and data acquisition(“SCADA”). These primary power distribution analyzing systems, however,are complex, expensive, and fail to adequately analyze power that isdelivered to the industrial, commercial, or residential customer sitesthrough the secondary power distribution system.

Also, various systems and methods of metering power which are known tothose skilled in the art are used by commercial, industrial, andresidential customers of power utility companies. These power meteringsystems, however, generally only measure the amount of power used by thecustomer and record the usage for reading at a later time by the utilitypower company supplying the power to the customer. A revenue accuracymeter is an example of such a metering system conventionally positionedat a customer site to receive and measure the amount of power consumedby the customer during predetermined time periods during a day.

Conventionally, electric power is delivered to industrial, commercial,and residential customers by local or regional utility companies throughthe secondary power distribution system to revenue accuracy typeelectricity meters as an alternating current (“AC”) voltage thatapproximates a sine wave over a time period and normally flows throughcustomer premises as an AC current that also approximates a sine waveover a time period. The term “alternating waveform” generally describesany symmetrical waveform, including square, sawtooth, triangular, andsinusoidal waves, whose polarity varies regularly with time. The term“AC” (i.e., alternating current), however, almost always means that thecurrent is produced from the application of a sinusoidal voltage, i.e.,AC voltage.

In an AC power distribution system, the expected frequency of voltage orcurrent, e.g., 50 Hertz (“Hz”), 60 Hz, or 400 Hz, is conventionallyreferred to as the “fundamental” frequency, regardless of the actualspectral amplitude peak. Integer multiples of this fundamental frequencyare usually referred to as harmonic frequencies, and spectral amplitudepeaks at frequencies below the fundamental are often referred to as“sub-harmonics,” regardless of their ratio relationship to thefundamental.

Various distribution system and environmental factors, however, candistort the voltage waveform of the fundamental frequency, i.e.,harmonic distortion, and can further cause spikes, surges, or sags, andother disturbances such as transients, time voltage variations, voltageimbalances, voltage fluctuations and power frequency variations. Suchevents are often referred to in the art and will be referred to hereinas power quality disturbances, or simply disturbances. Power qualitydisturbances can greatly affect the quality of power received by thepower customer at its facility or residence.

These revenue accuracy metering systems have been developed to provideimproved techniques for accurately measuring the amount of power used bythe customer so that the customer is charged an appropriate amount andso that the utility company receives appropriate compensation for thepower delivered and used by the customer. Examples of such meteringsystems may be seen in U.S. Pat. No. 5,300,924 by McEachern et al.titled “Harmonic Measuring Instrument For AC Power Systems With ATime-Based Threshold Means” and U.S. Pat. No. 5,307,009 by McEachern etal. titled “Harmonic-Adjusted Watt-Hour Meter.”

These conventional revenue accuracy type metering systems, however, havefailed to provide information about the quality of the power received bya power customer at a particular customer site. Power qualityinformation may include the frequency and duration of power qualitydisturbances in the power delivered to the customer site. As utilitycompanies become more and more deregulated, these companies will likelybe competing more aggressively for power customers, particularly heavypower users, and therefore information regarding the quality of thepower received by the power customer is likely to be important.

For example, one competitive advantage that some utility companies mayhave over their competitors could be that their customers experiencerelatively few power quality disturbances. Similarly, one company maypromote the fact that it has fewer times during a month that powersurges reach the customer causing potential computer systems outages atthe customer site. Another company may promote that it has fewer timesduring a month when the voltage level delivered to the customer is notwithin predetermined ranges which may be detrimental to electromagneticdevices such as motors or relays. Previous systems for measuring qualityof power in general, however, are expensive, are bulky, require specialset up and are not integrated into or with a revenue accuracy meter.Without a revenue accuracy metering system that measures the quality ofthe power supplied to and received by the customer, however, comparisonsof the quality of power provided by different suppliers cannot readilybe made.

One solution to the above described problems is proposed by U.S. Pat.No. 5,627,759 to Bearden et al. (hereinafter the “Bearden patent”),which is assigned to the assignee of the present invention andincorporated herein by reference. The Bearden patent describes a revenueaccurate meter that is also operable to, among other things, detectpower quality events, such as a power surge or sag, and then report thedetection of the power quality event to a utility or supplier.

One of the useful features of the meter disclosed in the Bearden patentis waveform capture. The meter of the Bearden patent is operable toobtain waveform information regarding the voltage and/or currentwaveform at about the time a power quality event is detected. Such afeature is advantageous because the captured waveform may be analyzed tohelp determine potential causes of the event, the severity of the event,or other pertinent data. While the waveform capture feature disclosed bythe Bearden patent contributes to the usefulness of the meter, theincreased sophistication of power consumers has created a need forfurther information retrieval capabilities in power quality measurementdevices.

In particular, it has been found that much may be learned about a powerquality event by analyzing the voltage waveform when the power qualityevent ends, as well as when it begins. Moreover, it has been found thatpower quality events can often include one or more “sub-events”. Forexample, consider a power quality event in the form of a voltage sagwherein the line voltage falls from 120 volts to 100 volts for fiveminutes, and then falls to 85 volts for two hours, and then returns to100 volts for an hour, and then returns to 120 volts. It is useful togather information about such sub-events for analysis of the powerdistribution system.

One solution would be to implement a power quality device that capturesall the voltage waveform data at all times. However, capturing all suchdata is impracticable. In particular, in order to be of use, the voltagewaveform data must be captured, or in other words, stored innon-volatile memory for subsequent retrieval and analysis. The totalityof waveform data for any significant length of time over one second issubstantial. For example, at a sampling rate of 32 samples per cycle,one seconds worth of data for a single voltage waveform constitutes 1920samples of data per second. For poly-phase meters wherein both voltageand current are sampled, the number of samples is four to six times thatnumber.

It is thus apparent that the storage of ongoing waveform data cannot beachieved in non-volatile memory contained within the meter for anysignificant period of time. Moreover, it is impracticable for the meterto communicate such data to a remote device having greater memorycapability. In particular, the communication of such amounts of datarequires a substantial amount of constantly available communicationbandwidth, which is not cost-effective nor practical.

What is needed, therefore, is a power measurement device which iscoupled with a revenue accurate meter and has the capability to obtainwaveform information for multiple phenomena within a power qualityevent. In particular, there is a need for such a device that obtainswaveform information for both the beginning and the end of a powerquality event, as well as for a device that obtains waveform informationfor a plurality of sub-events within a particular power quality event.

SUMMARY OF THE INVENTION

The present invention addresses the above needs, as well as others, byproviding a system and method for use in a revenue accurate meter thatdetects a variation in the line voltage level from a normal voltagelevel, capturing the line voltage waveform corresponding to the timewhen the variation was detected, detecting a reduction in the variationof the line voltage level from the normal voltage level, and capturingthe waveform corresponding to the time the reduction of the variationwas detected. By capturing waveforms both at the time that the voltagevaries from the norm and the time that the voltage returns to the norm,the present invention obtains further detailed information about a powerquality event than that available in the prior art. Moreover, bycapturing waveforms corresponding to the times that the voltagevariation is detected and the time that the reduction in the variationis detected, storage and/or communication of the captured waveform datais practicable. Such data may then be analyzed at a later time and/or ata remote location to obtain information regarding the disturbance thatcaused the line voltage variation.

An exemplary method according to the present invention is carried outwithin an electrical energy meter containing means therein for meteringa quantity of electrical energy generated by a supplier and transferredvia a power supply line to a load of a customer during an energymeasurement time interval. The exemplary method is a method ofmonitoring variations in the metered quantity of electrical energy.

The method includes a first step of sensing a line voltage transferredvia the power supply line to the load during the energy measurement timeinterval. The method also includes the step of detecting a variation ina magnitude of the sensed line voltage relative to an acceptable voltagelevel, wherein said variation exceeds a first variation threshold. Themethod then includes the step of capturing a first waveform of thesensed line voltage corresponding to the time when said variation isdetected. Finally, the method includes the steps of detecting asubsequent reduction in the variation of the magnitude of the sensedline voltage such that the variation is equal to or less than the firstvariation threshold and capturing a second waveform of the sensed linevoltage corresponding to the time when the subsequent reduction in thevariation is detected.

An exemplary apparatus according to the present invention is anelectrical energy meter for obtaining data regarding line voltagevariations in real-time. The electrical energy meter includes a voltagedigitizing circuit, a current digitizing circuit, a metering circuit anda power quality circuit. The voltage digitizing circuit is operable toobtain analog line voltage information and generated digital linevoltage information therefrom. The current digitizing circuit isoperable to obtain analog line current information and generate digitalline current information therefrom. The metering circuit is operable toreceive the digital line voltage information and the digital linecurrent information and generate metering information therefrom.

The power quality circuit is operable to: receive the digital linevoltage information and obtain magnitude information therefrom, themagnitude information representative of the magnitude of the linevoltage; detect a variation in the magnitude of the line voltagerelative to an acceptable voltage level wherein said variation exceeds afirst variation threshold; capture a first waveform in the form of afirst set of digital line voltage information corresponding to the timewhen said variation is detected; detect a subsequent reduction in thevariation of the magnitude of the line voltage such that the variationis equal to or less than the first variation threshold; and capture asecond waveform in the form of a second set of digital line voltageinformation corresponding to the time when the subsequent reduction inthe variation is detected.

The exemplary method and apparatus described above provide the abovementioned advantages of capturing waveform information for a voltagewaveform at both the beginning of a power quality event and the end of apower quality event. In alternative embodiments, the method andapparatus may be configured to detect a second variation that is greaterthan the first variation, and capture a waveform corresponding to thetime when the second variation is detected. Such a method and apparatuswould then be capable of capturing waveform data on sub-events within apower quality event.

The above features and advantages, as well as others, will become morereadily apparent to those of ordinary skill in the art by reference tothe following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B schematically illustrate an environmental view of arevenue accuracy meter having power quality measurement according to thepresent invention;

FIGS. 2A and 2B schematically illustrate a revenue accuracy meter havingpower quality measurement arranged in communication with a powergenerator and a power customer according to the present invention;

FIG. 3 schematically illustrates a revenue accuracy meter having powerquality measurement arranged in communication with various datacommunication links according to the present invention;

FIG. 4 illustrates a revenue accuracy meter having power qualitymeasurement according to the present invention;

FIGS. 5A and 5B schematically illustrate a flow chart of a digitalsignal processor circuit of a revenue accuracy meter having powerquality measurement according to the present invention;

FIG. 6 schematically illustrates a power quality measurement circuit ofa revenue accuracy meter according to the present invention;

FIGS. 7A, 7B, and 7C illustrates the operations of a power qualitycircuit within the revenue accuracy meter of FIG. 3 in accordance withthe present invention;

FIG. 8 schematically illustrates a revenue accuracy meter having powerquality measurement and energy management according to a secondembodiment of the present invention; and

FIG. 9 schematically illustrates an apparatus for providing controlparameters to the revenue accuracy meter of FIGS. 3 and 4 in accordancewith the present invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings in which preferred embodiments ofthe invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theillustrated embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be thorough and complete and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout.

As illustrated in the schematic environmental view of FIGS. 1A and 1B,utility power distribution 20 generally starts with generation of thepower by a power generation facility 21, i.e., power generator or powerplant. The power generator 21 supplies power through step-upsubtransmission transformers 21 b to transmission stations 23. To reducepower transportation losses, the step-up transformers 21 b increase thevoltage and reduce the current. The actual transmission line voltageconventionally depends on the distance between the subtransmissiontransformers 21 b and the users or customers, i.e., commercial,industrial, or residential 37, 38. Distribution substation transformers25, 26, 27 reduce the voltage from transmission line level generally toa range of about 2-35 kilo-volts (“kV”). The primary power distributionsystem 31 delivers power to distribution transformers 28, 28 a thatreduce the voltage still further, i.e., about 120 V to 600 V.

Conventionally, power utility companies and suppliers have developedsystems to analyze and manage power generated and power to be deliveredto the transmission lines in the primary power distribution system 31,e.g., primarily through supervisory control and data acquisition(“SCADA”) at a remote operations center 22 such as illustrated. Theseoperation centers 22 generally communicate with the generationfacilities 21 and the substations 24, 25 through conventional datacommunication terminals 21 a, 24 a, 25 a. Because problems currentlyarise in the secondary power distribution system 36, i.e., from thedistribution substation to the customers, with respect to analyzingpower that is delivered to the industrial, commercial, or residentialcustomer sites through the secondary power distribution system 36, arevenue accuracy meter 40, or a plurality of revenue accuracy meters 40is provided having power quality measurement according to the presentinvention and preferably is positioned as illustrated (FIGS. 1A-1B) inthe secondary power distribution system 36 to provide a remote terminalor node in the overall system 20 for troubleshooting or diagnosingproblems, identifying emergency situations, and systematically analyzinginformation from specific customer sites.

Due to the deregulation of the power delivery industry and theconsequent brokering of power at the transmission level, it is alsoadvantageous to implement revenue accurate meters 40 having powerquality measurement according to the present invention within thetransmission system 31 and/or generation system 21.

FIGS. 2A, 2B, 3, and 4 schematically illustrate a revenue accuracy meter40 having power quality measurement arranged in communication with apower generator 80 such as a utility power company and a power customer60 according to the present invention. A revenue accuracy meter 40according to the present invention is an electricity meter or analternating current static watt-hour meter used for billing functions,i.e., billing meter. These revenue power or electricity meterspreferably are solid state meters that at least meet American NationalStandards Institute (“ANSI”) 12.16, International ElectrotechnicalCommission (“IEC”) 687/1036 standard, similar improved or revisedstandards, or the like, as understood by those skilled in the art. Asillustrated, the revenue accuracy meter 40 for measuring the amount andquality of electrical power received by a power customer 60 preferablyhas a housing 40 a and a communications interface which preferablyincludes a plurality of data communication ports 41, 42, 43, 44positioned in the housing 40 a (see FIGS. 3 and 4A). The housing 40 a isconfigured as is well known in the art to connect the meter 40 to thepower lines through, for example, a meter socket.

Although four data communication ports 41, 42, 43, 44 are illustrated, arevenue accuracy meter 40 according to the present invention preferablyhas at least two data communications ports. At least one of theplurality of data communication ports 41, 42, 43, 44 is arranged fordata communications with a power customer 60, e.g., a power customerport 41, and at least one of the plurality of data communication ports41, 42, 43, 44 is arranged for data communications with a powergenerator, e.g., power generator ports 42, 43, 44.

The particular embodiment of the ports 41, 42, 43, 44 illustrated,however, advantageously provides real time data communications with aplurality of the various groups or departments of a utility company 80such as marketing 82, operations 83, engineering 84, and/orbilling/finance 85 (FIG. 2B). For example, power quality data such asthat discussed below in connection with FIGS. 6, 7A, 7B, and 7C may beutilized by the customer service or the marketing group 82 receivingdata from a revenue accuracy meter 40 according to the present inventionby monitoring power outage, sags/surges, and excessive harmonics. Thisinformation can then be relayed, i.e., by sequential calls, to a headoffice, key account representatives, and/or customers 60. Such powerquality data may be utilized by operations 83 to monitorvoltage/current, KW/KVAR, disturbances, and/or harmonics received bycustomers 60 through the meter 40 and to monitor transformers, i.e.,temperature, capacitors, and other control functions in the powerdistribution system 20.

The engineering group or department, for example, may utilize the meter40 and the data received therefrom for monitoring total harmonicdistortion, for captured waveform analysis, for spectral analysis, aswell as studying and analyzing outages and sags/surges from a diagnosticapproach. The billing or finance group 85, in turn, may conduct load orrate research based upon information provided from the meter 40 aboutpower quality and power usage. As understood by those skilled in theart, the billing group 85 of the power generator 80, for example, canconduct TOU metering, real-time pricing, transformer loss, compensation,load profile, meter installation integrity, meter wiring verification,load curtailment, and/or various other functions. Also, these variousgroups of the power generator 80 can also responsively interact with thesubstation controller 86 such as in multi-drop meter applications or tocommunicate with remote terminal units (“RTUs”), printers, or the like.Further, the power generator 80 can provide various auxiliary inputs tothe meter 40 such as transformer oil temperature data, feeder subloads,redundant metering data, status alarms, pressure data, and/or otherinformation as desired.

The customer, on the other hand, can receive on-line data such asengineering units, energy cost, subload data, alternate utility data,and other totals or specific information as needed. Preferably the meter40 also has customer programmed relay control with security, utilityalarming, demand prediction, and energy management capabilities.Additionally, as also illustrated in FIGS. 2A and 8A, a revenue accuracymeter 40 according to the present invention further has an energymanagement controller 90 electrically connected to the second receiverand the second transmitter for controlling power usage responsive topredetermined command signals received from the power customer throughthe power customer port of the communications interface. Likewise, thecustomer may provide auxiliary inputs 62 to the meter 40 such as alarms,status, production parameters, non-electrical utility data, loadcurtailment data, subload data, as well as other data as desired. Themeter 40 may also be monitored or utilized by the customer at a customercentral station 61 as illustrated. The data communication ports alsoprovide inter or intra-customer communication, i.e., customer to utilityor other customer and communication within customer facility orlocations.

Either separate from the energy management controller 90 or inconjunction therewith, a meter 40 according to the invention preferablyfurther has an access restricter, not shown, coupled in electricalcommunication with the power generator port for providing restrictedaccess between the power customer port and the power generator port.This security access preferably is resident in one of the controllers ofthe meter 40. This access restriction means or access restricterpreferably is software programmed as understood by those skilled in theart so that access is provided to either the power customer or the powergenerator by a command signal representative of a user password or adata access key. This, in turn, provides a wall for security betweenmeter functions used by a customer 60 and meter functions used by apower generator or other third party 80.

Although, as understood by those skilled in the art, the communicationinterface of a revenue accuracy meter 40 may include any means forcommunicating data to and from the meter 40, such as using a probingdevice, an optical device, or a remote device for interfacing with themeter 40, the communications interface of a revenue accuracy meter 40preferably includes one or more transceivers, e.g., universalasynchronous receiver/transmitter (“UART”), positioned within thehousing 40 a of the meter 40 and arranged to receive and transmit datasignals through the data communication ports 41, 42, 43, 44.

Referring now to FIG. 3 in particular, the exemplary embodiment of themeter 40 includes an analog sensor circuit 51, a digital signalprocessing circuit 45, a circular buffer 52, a microprocessor 48, anon-volatile memory 53, a time standard source 54, a communicationinterface circuit 55, a display 56, a clock circuit 57 and the ports 41,42, 43 and 44.

The analog sensor circuit 51 is a circuit that connects to the utilitypower lines and is operable to generate signals including analog linevoltage information and analog line current information for each of thephases in a polyphase power system. In the exemplary embodimentdescribed herein, the analog sensor circuit 51 is operable to obtainanalog line voltage information, VA, VB and VC, and analog line currentinformation, IA, IB and IC for three phases of a three phase electricalsystem. To this end, the analog sensor circuit may suitably includevoltage divider circuits, current shunts, current transformers, embeddedcoils, and/or other well known voltage and current multiple outputssensing technology.

The digital signal processing (“DSP”) circuit 45 and the microprocessor48 together comprise a metering circuit that is operable to receive linevoltage and line current information from the analog sensor circuit 51and generate metering information therefrom. In particular, the DSPcircuit 45, in addition to a DSP, includes one or more analog to digitalsignal converters that receive the analog line voltage information andanalog line current information and generate digital line voltageinformation and digital line current information therefrom. The DSPcircuit 45 and microprocessor 48 are furthermore suitably programmed toreceive the digital line current information and digital line voltageinformation from the analog to digital converters and generate meteringinformation therefrom. The metering information includes watts, VAR andVA quantities representative of energy consumed by the customer. Furtherdetail regarding the operation of the metering circuit is describedbelow in connection with FIGS. 5A and SB.

The DSP circuit 45 and the microprocessor 48 also together comprise apower quality circuit operable to capture waveforms in accordance withthe present invention. Further detail regarding the operation of thepower quality circuit is described below in connection with FIGS. 6, 7A,7B, and 7C.

It will be noted that the architecture of the metering circuit and powerquality circuit describe above is given by way of example only. Those ofordinary skill in the art may readily devise alternative architecturesthat incorporate the principles of the metering circuit and powerquality circuit described herein. For example, the use of a combinationof a DSP circuit and a microprocessor as the metering circuit and powerquality circuit is given by way of example only. A single processor maysuitably be used for either or both of such circuits. Such a singleprocessor may require relatively high processing speeds to accomplishrevenue quality metering and therefore may not be as cost effective asthe architecture discussed herein. Alternatively, those of ordinaryskill in the art may employ metering circuits and/or power qualitycircuits according to the present invention that incorporate three ormore processors, or that incorporate different types of controllers andprocessors. Such architectures would provide at least some of theadvantages of the present invention.

The power quality circuit of the meter 40 further includes the circularbuffer 52. The circular buffer 52 is a circuitous memory structurewithin at least a portion of a memory device, preferably RAM. Thecircuitous memory structure stores digital line voltage and/or digitalline current values in the sequence in which they are received. Once thecircular buffer 52 is full, each new value entered replaces the oldestvalue in the buffer. In the present invention, the circular buffer 52may suitably be an allocated portion of the internal RAM of the DSPcircuit 45. However, the circular buffer 52 may alternatively comprisean external RAM or even RAM that is internally or externally coupled tothe microprocessor 48.

Returning to the exemplary embodiment of the meter 40 illustrated inFIG. 3, the non-volatile memory 53 may suitably be a flash memorynon-volatile RAM, EEPROM, or other non-volatile memory. Non-volatile RAMand flash memory are preferable because the footprint of such memoriesper unit of memory is significantly smaller than the footprint ofEEPROM. However, EEPROM can be advantageous when battery back-up orother back up power sources are impractical or unreliable. Preferably,the non-volatile memory 53 has 4 to 8 megabytes of memory.

The time standard source 54 is a source of externally-generatedprecision time standard information. For example, the time standardsource 54 may suitably be a GPS receiver operable to obtain precisiontime standard information via satellite. Alternatively, the timestandard source may be an IRIG or WWV time standard receiver. An exampleof a time standard source that may be incorporated into the meter 40 isthe model GPS-PCI card available from TrueTime, Inc.

The clock circuit 57 is a circuit well-known in the art that is operableto generate clock/calendar information in an ongoing manner. In general,the clock circuit 57 may suitably include a crystal oscillator circuitand appropriate logic gates and counters for generating clock/calendarinformation based on the crystal oscillator circuit. Such circuits arewell known. The clock circuit 57 is coupled to the microprocessor toprovide the clock/calendar information thereto. The clock circuit 57 isfurther operably connected, through the microprocessor 48, to receivethe externally generated precision time information from the timestandard source 54. The clock circuit 57 is operable to adjust itsclock/calendar information based on the received externally generatedprecision time information. In accordance with the exemplary embodimentdescribed herein, the time standard source 54 provider precision timeinformation in the form of pulse, i.e. one pulse per second. Thus, theclock circuit 67 is “recalibrated” each time it receives a pulse.

The display 56 is an LCD or other display circuit operable to displaydata provided by the microprocessor 48. The display 56 and/or themicroprocessor 48 includes any necessary drivers for converting themicroprocessor data into signals that cause the LCD or other displaymedium to display the information contained in the data. Such circuitsare well known.

The communication interface circuit 55 cooperates with the communicationports 41, 42, 43, and 44 to effectuate communication between the meter40, through the microprocessor 48, and external devices, includingremotely located external devices. To this end, the communicationinterface circuit 55 may include one or more additional processors thatassist in providing such communications.

The ports 41, 42, 43 and 44 preferably include an RS-232 interface portand/or a 20 milliampere (“mA”) current loop, an optical port, and two ofeither an internal modem, a direct interface, a protocol converter, oran RS-485 port. The internal modem is arranged for communicating withutility customer or power customer auxiliary inputs and outputs. Thedirect interface (“I/F”) is arranged to connect to an external modemwhich may provide either additional or duplicative data to theprocessors 45, 48. The protocol converter and the RS-485 port arelikewise arranged to provide data communication to the operations center22 (see FIG. 1) as well as the local area network (“LAN”) of the utilitycompany or industrial consumer. The optical port preferably is arrangedfor data communication through a power generator port to laptopcomputers or the like. The current loop provides secure datacommunication and, preferably, is arranged for data communication withthe auxiliary inputs 81, 85 from the utility 80, such as an encoder,printer, RTU, various software or hardware tools, personal computer,remote data display, or the like. The external modem and the LAN areconnected in electrical communication with the desired group 82, 83, 84,86 of the utility or power generator 80 as illustrated.

The elements of the meter 40 described above of FIG. 3 areadvantageously configured to reside within a single housing that isoperable to be mounted on select ones of standard meter sockets, asillustrated in FIG. 4.

FIGS. 5A and 5B show in further detail the operation of the meteringcircuit and the power quality circuit of the meter 40 of FIG. 3. Inparticular, the DSP circuit 45 portion of the metering circuit and powerquality circuit is shown in detail in FIGS. 5A and 5B. In general, theDSP circuit 45 receives the analog line voltage information and analogline current information and performs the preliminary meteringcalculations as well as preliminary power quality determinations asdescribed herebelow. With respect to metering calculations, the DSPcircuit 45 samples and processes the analog line voltage and currentsignals using high computational speeds and generates interim valuessuch as accumulated watts, VA, and VAR values. By way of example, theDSP circuit 45 samples each line voltage and line current signal 32times per second. This sampling rate, combined with the use of 20 bitresolution samples, allows the meter 40 to perform revenue accuratemetering measurements.

The microprocessor 48 periodically retrieves the accumulated interimvalues and uses them to generate standard meter energy pulses. Themicroprocessor 48 also accumulates various energy consumption values incompliance with metering standards. The microprocessor 48 furtheroperates to cause display of certain metering values and/orcommunication of metering values to the consumer or the utility.

The DSP circuit 45 further employs the sampled or digitized line voltagesignals, and in some cases the digitized line current samples, todetermine the presence of undesired variations in the electrical signalrepresentative of power received by a power customer 60 acrosselectrical power lines or the like such as spikes, surges, sags,harmonic distortion, and/or other disturbances. The variationdetermining means preferably is a variation determiner, or other powerquality circuit 200, as illustrated coupled in electrical communicationwith the receiver for determining frequency, i.e., time periods or timeoccurrences, and duration of undesired variations in the receivedvoltage signal during a plurality of predetermined time periods. Theseundesired signal variations are preferably minimum or maximum thresholdvariations and/or timing frequency variations of the supplied signal.The operation of the power quality circuit is discussed in furtherdetail in connection with FIG. 6.

Once an undesired signal variation is detected, information is passed tothe microprocessor 48 which controls the communication and/or storage ofinformation regarding the variation, including waveform capture inaccordance with the present invention, as described below in connectionwith FIGS. 7A, 7B and 7C.

As best illustrated in FIGS. 5A and 5B, the DSP circuit 45 receivesanalog line voltage information VX and analog line current informationIX which is representative of the power received by a power customer onone phase of a polyphase system. In a three phase system, the DSPcircuit 45 receives the line current information and line voltageinformation of each phase in sequential manner. To this end, the analogline current and analog line voltage information is multiplexed so thatonly one line voltage VX and only one line current IX is received at anyparticular instant. It will be noted that in the alternative, thecircuit shown in FIG. 5A may suitably be duplicated for each of thephases of the system.

In any event, the sample and digitize circuit 111, which is preferablyan A/D converter, converts IA to a digital line current signal.Likewise, the sample and digitize circuit 101, which is also preferablyan A/D converter, converts VA to a digital line voltage signal. Timecompensators 102, 112 then compensate for time skew in sampling due tomultiplexing a single analog-to-digital converter. The time compensators102, 112 may suitably be short FIR or smoothing filters withnonsymmetrical coefficients to get the proper time skew with areasonably flat frequency response.

Alternatively, time compensators 102, 112 may be omitted ifsimultaneously sampling A/D converters are used. In such a case,measurement alignment is achieved through synchronization of the A/Dconverters.

In any event, the compensated digital signals then are respectivelyreceived by low pass filters 103, 113. The digital line current signalpasses through a fixed high pass filter 114 and the digital line voltagesignal passes through an adjustable high pass filter 104. A calibrationfactor 115, 135 is then respectively applied to the filtered signals.After calibration, the digital line current signal and the digital linevoltage signal is applied to the power quality circuit 200 of the meter40 according to the present invention. As understood by those skilled inthe art, the power quality circuit 200 preferably is in the form ofsoftware and/or hardware resident within or in electrical communicationwith the DSP circuit 45 and the microprocessor 48 of the presentinvention. FIGS. 6, 7A, 7B, and 7C illustrate the operations of thepower quality circuit 200 in further detail.

Once the power quality circuit 200 receives the digital line current anddigital line voltage information, the meter calculations are thenpreferably continued by initiating the start customer load detectors125, 145. As understood by those skilled in the metering art, thesedetectors 125, 145 preferably assure that relatively very small signals,i.e., due to leakage current, register as zero usage. The signal thenpasses through delay adjustments 126, 146 to lower the sampling rate,e.g., through decimation. The delay adjustments preferably allow thenormal power measurement process to run at a slower rate and thereforeuse less of the resources of the microprocessor 48 or DSP circuit 45.The signal passes to a system configuration block 147 to allow forspecial meter types such as a 2½ wye meter.

As illustrated in FIG. 5B, the signal further passes through a filteringconfiguration 162 preferably such as illustrated. The current signalpreferably is applied to a low pass filter 103A. This filter 103Aproduces a phase shift that approaches 90 degrees lag as the frequencyof the amplitude signal increases. This filter 103A also produces anamplitude response that decreases with frequency, which is compensatedby the two FIR filters 103B and 104A as illustrated. The output of thevoltage FIR filter 104A is then applied to a low pass filter 104B.Because the VAR measurement preferably may require a 90 degree lag ofvoltage relative to current, as understood by those skilled in the art,and the current is lagged by 90 degrees already, an additional lag of180 degrees is needed in the voltage. A signal inversion by an inverter104D preferably supplies this lag. The output of multiplier 129 thusprovides VARs with errors due to 103A only approaching 90 degrees.Multiplier 128 produces an error correction signal of the correct leveland phase to correct the errors when summed in summer block 148.

The scalers 103C, 104C, and 104E preferably adjust signal levels so thatwatts and VARs have the same scale factors in the system 162. Theoutputs of multipliers 151, 154, 161, and 192 are therefore amperessquared, watts, volts squared, and neutral amps squared as measured byconventional metering. Multipliers 172, 175 and 182 preferably havetheir input 60 Hertz fundamental removed by filters 171 and 181 so thattheir outputs are the harmonic amperes squared, harmonic watts, andharmonic volts squared. As illustrated by FIG. 5B, multiplier 192 alsohas as its input the output of a 3-phase current summer 191. Thesevalues or quantities are then integrated in accumulators 152, 155, 163,165, 173, 176, 183, 193, 197 and copied into buffers 153, 156, 164, 166,174, 177, 184, 194, 198. In addition, the harmonic amperes for the threephases are summed and multiplied (Blocks 195, 196) to generate harmonicneutral current squared. The original signal prior to the filter is alsochecked at block 158. The zero cross signal from block 158 causes theaccumulator copies 153, 156, 164, 166, 174, 177, 184, 194, 198 to havean integer number of cycles such as for stable short term readings.

The microprocessor 48 then periodically retrieves the values from thebuffers 153, 156, 164, 166, 174, 177, 184, 194 and 198 and generates themetering quantities therefrom. In particular, the microprocessor 48accumulates watts, VAs, VARs and performs other energy-relatedcalculations known in the art. Once the values have been retrieved fromthe buffers, the buffers 153, 156, 164, 166, 174, 177, 184, 194, and 198are cleared.

FIG. 6 illustrates a power quality circuit 200 of the inventionillustrated in the form of a variation determiner. The power qualitycircuit 200 at its input receives per phase digital line voltageinformation (and/or digital line current information) in the form ofdigital samples. It will be noted that the power quality circuit 200segregates each phase such that each of the below operations isperformed individually for each phase.

The digital samples are provided to both the circular buffer 52 and thescaler 210 of the variation determiner. In particular, each digital linevoltage sample is provided to the circular buffer 52 prior to furtherprocessing within the variation determiner. The circular buffer 52stores the most recent NN samples, where NN is a predetermined number,typically defined by an operator and programmed into the meter. Furtherdetail regarding the programming of values into the meter 40 isdiscussed below in connection with FIG. 9. The circular buffer 52therefore, at any time, contains digital line voltage informationrepresentative of the line voltage waveform for the most recent MMcycles, where MM=NN/(samples per cycle).

In an alternative embodiment, a data compression function may beintroduced at the input of the circular buffer 52. The data compressionfunction could be any suitable data compression algorithm and wouldreduce the amount of samples required to represent the waveform shape.The use of such a data compression function would thereby conservememory space, albeit at the cost of processing power.

In any event, the scaler 210, which also receives the digital linevoltage information, provides the scaled digital line voltage signal toa summation device 111. The scaler 210 preferably scales the size of thesignal to assure against math overflows. The scaler 210 also preferablysquares the signal so as to make the meter responsive to root meansquare (“RMS”) voltage. The scaled signal is then summed at thesummation device 211. A voltage cycle time determiner 212 is coupled inelectrical communication with the scaler and/or squarer 210, i.e.,through the summation device 211, for determining voltage cycle time.Half-cycle timing 213 and waiting 214 periods are preferably forsynchronizing or zeroing the sum 215 of the timing of the system 200.Accumulation preferably occurs for one-half cycle, passes the result toan FIR filter 216, then clears the accumulator, i.e., S=0.

The multiple tap FIR filter 216, i.e., preferably includes 1-6 taps, andis coupled in electrical communication with the cycle time determiner212 for smoothing and/or filtering the voltage squared signal. Thenumber 216 a and the coefficients 216 b for the taps are input into theFIR signal smoothing device 216. It will also be understood that theelectrical signals as illustrated in FIGS. 6-7C of the power qualitycircuit 200 are illustrative for the voltage signals, but underappropriate current signal characterization parameters may also includethe current signals.

The output of the FIR signal smoothing device 216 is then provided to avoltage handler 230. The voltage handler 230 is the block that comparesthe resultant value with expected values to determine if a line voltagevariation is present. More importantly, the voltage handler 230determines whether a detected line voltage variation exceeds one or morevariation thresholds and causes waveform capture in accordance with thepresent invention. In addition, once such a variation is detected, thevoltage handler 230 subsequently determines when the variation reducesto a point where it no longer exceeds one or more thresholds and causesfurther waveform capture in accordance with the present invention. Tothis end, the voltage handler 230 in the exemplary embodiment describedherein operates as described below in connection with FIGS. 7A, 7B, and7C.

The flow diagram illustrated in FIGS. 7A, 7B, and 7C illustrate thesteps of the variation detection and waveform capture operations of theexemplary embodiment of the present invention. It is noted that the mostof the operation of the voltage handler 230 as illustrated in FIGS. 7A,7B, and 7C is preferably carried out in the DSP circuit 45, which isdesigned to readily handle calculations at the sample rate required forthe revenue accurate metering circuit operation. However, because theoperations of the voltage handler 230 in the present embodiment requirethe voltage measure for an entire half cycle, the operations aresuitably slow enough to be carried out by the microprocessor 48 ifdesired. In some cases, it may be preferable to have a combination ofthe DSP circuit 45 and the microprocessor 48 carry out the operations ofthe voltage handler 230.

In any event, referring to FIG. 7A, the voltage handler 230 firstreceives the voltage magnitude information, represented herein as thevalue VOLT, from the FIR smoothing circuit 216 (step 305). The voltagehandler 230 then determines whether the variation of VOLT from anexpected value exceeds a first variation threshold (step 310). If so,then the voltage handler 230 proceeds to step 320. If not, however, thenthe voltage handler 230 proceeds to step 315.

In particular, in step 310, the voltage handler 230 compares VOLT to aset point level, which may be a high set point level or a low set pointlevel. The high set point level represents a voltage magnitude level (inthe same units as VOLT) above which a potential waveform capture eventis identified. Typically, the high set point level corresponds to avoltage level that, if maintained for several half-cycles, indicates apower quality event. Likewise, a low set point level represents avoltage magnitude level below which a potential waveform capture event(i.e. power quality event) is identified. Thus, for example, if thenominal or expected line voltage level is 120 volts, then a low setpoint level may be set to correspond to a detected line voltage of 90volts. Set point levels may either be preset or programmed into themeter 40 by the programming device 600 discussed below in connectionwith FIG. 9.

In the preferred embodiment discussed herein, the programming device 600may be used to set multiple points both for high set points and low setpoints. The second set point may suitably identify a sub-event within apower quality event, such as a further voltage sag, that occurs within apower quality event identified by the first set point. Accordingly, itcan be seen that several layers of set points, both below the expectedline voltage level and above the expected line voltage level may beemployed.

In any event, if the variation of VOLT exceeds the first variationthreshold (or in other words, VOLT is greater than a first high setpoint or less than a first low set point), then an index of consecutivevariations N is incremented (step 320). If, however, the variation ofVOLT does not exceed the first variation threshold, then the index N isreset to zero (step 315) and the voltage handler 230 returns to step 305and proceeds accordingly with the next value received from the FIRsmoothing filter 216.

Referring again to step 320, after the index N is incremented, thevoltage handler 230 determines whether N exceeds a predeterminedvariation duration value (step 325). The variation duration valuerepresents a minimum number of half-cycles that the variation of VOLTmust exceed the first variation threshold to trigger the waveformcapture. The predetermined value is set such that a spurious transientthat is insignificant from a power quality standpoint will not trigger awaveform capture and other power quality event recording and reportingfunctions. To this end, the predetermined valve may be 2, 4, or 6half-cycles. The predetermined value may suitably be set by an operator.

It will be noted that other techniques for distinguishing betweenspurious variations and real power quality events may be used. Forexample, FIGS. 7A, 7B, and 7C of U.S. Pat. No. 5,627,759 illustrate infurther detail such a technique that may be incorporated into the meter40 described herein.

In any event, if the voltage handler 230 determines that N does notexceed the predetermined variation duration value, then the voltagehandler returns to step 305 to receive the next voltage magnitude valueand proceed accordingly.

If, however, N exceeds the predetermined variation duration value, thenthe voltage handler resets N (step 330) and records the time and date ofthe power quality event (step 335). In particular, the time and dateinformation provided by the clock circuit 57 is written immediately to abuffer signifying the detection of a waveform capture event.

The voltage handler 230 also retrieves the circular buffer contents. Thecircular buffer contents include the previous MM cycles worth ofhistorical waveform sample data. The voltage handler 230 then forms apower quality event record. The power quality event record may suitablybe a time value series data structure that includes the circular buffercontents and the time and date information.

The voltage handler 230 then writes the record to a memory and/orcommunicates the record to the utility customer or the utility generatoror supplier (step 345). In particular, the voltage handler 230 may causethe record to be stored in either a memory that is inherent to eitherthe DSP circuit 45 or the microprocessor 48, or an external memory, notshown. Such a memory may suitably be a random access memory or asequentially accessed memory. However, it is preferable that at leastsome power quality event records be written to the non-volatile memoryin order to preserve the data upon loss of power to the meter.

Thus, each time the line voltage magnitude exceeds the first variationthreshold for N half-cycles, the buffer contents are recorded, or inother word, the line voltage (or line current) waveform is captured, bygeneration of the power quality event data record.

It is noted that it is also preferable to obtain data representative ofseveral waveform cycles that occur after the power quality event isfirst detected in step 335. To this end, the voltage handler 230 mayexecute a subprocess in which the requisite number of additional linevoltage samples are provided to the power quality event data record. Thenumber of line voltage samples to be recorded after detection of avariation that exceeds the first variation threshold also is programmedinto the meter 40 by an operator.

It will thus be noted that the waveform that is captured after detectionof the variation exceeding the first variation threshold may consist of:digital line voltage information corresponding to a predetermined amountof time before and up to the detection; digital line voltage informationcorresponding to the time of the detection to a predetermined amount oftime after the detection; or digital line voltage informationcorresponding to a predetermined time before to a predetermined timeafter the detection. In this manner, the waveform information directlysurrounding the time a power quality event occurs is captured forsubsequent analysis.

The use of a precision time standard clock provides a further advantageof allowing several meters having the capability of the meter 40 torecord power quality event data having time stamps that are completelysynchronized. For example, if a power quality event occurs and isdetected by four meters in a several mile radius, then the waveformscaptured at those four meters may be analyzed to determined how thepower quality e vent affected the power network. Because each of thefour meters employs a precision time standard clock, the capturedwaveform data from each meter can be corresponded exactly to waveformsfrom the other meters. Such information allows analysis of how aparticular problem propagated through the network as well as othervaluable power network analysis information.

In any event, after step 345, the voltage handler proceeds to step 350of FIG. 7B. The portion of the flow diagram in FIGS. 7B and 7Cillustrate an example of how end-of-event and sub-event waveform captureaccording to the present invention may be carried out. It is noted thatwhen the voltage handler 230 executes step 350, the meter 40 has alreadydetected and indeed is currently within a power quality event as definedby the first variation threshold.

At step 350, the voltage handler 230 again awaits and receives thevoltage magnitude information, VOLT, from the FIR smoothing circuit 216.The voltage handler 230 then determines whether the variation of VOLTfrom an expected value is less than the first variation threshold (step355). If so, then the voltage handler 230 proceeds to step 365. If not,however, then the voltage handler 230 proceeds to step 360. If thevariation is less than the first variation threshold, then it mayindicate that the present power quality event is ending and the linevoltage is returning to within normal parameters.

Specifically, if the variation is less than the first variationthreshold, then a second variation duration index L is reset to zero(step 360). The second variation duration index L is discussed infurther detail below in connection with steps 410 to 420. The voltagehandler 230 then increments the variation reduction duration index M(step 370). The voltage handler 230 then determines whether the index Mis less than a predetermined variation reduction duration value. Inparticular, similar to the detection of the first variation in steps 310to 325, the voltage handler 230 only records a reduction in thevariation of the line voltage from the first variation threshold ifthere are a predetermined number of half-cycles in which the variationis below the first variation threshold.

If M does not exceed the variation reduction duration value, then thevoltage handler 230 returns to step 350 to await further line voltageinformation. If, however, M exceeds the variation reduction durationvalue, then the voltage handler 230 performs the waveform captureoperations described below in connection with steps 380 through 395.Accordingly, the meter 40 of the present invention performs waveformcapture not only at the beginning of a power quality event, such as thatdetected in the operation of steps 330 through 345, but also at the endof a power quality event. To this end, the meter 40 performs waveformcapture both when a variation of the line voltage exceeds a variationthreshold and when the variation of the line voltage is reduced belowthe variation threshold.

In step 380, the voltage handler 230 resets M. The voltage handler 230then records the time and date of the power quality event (step 385). Inparticular, the time and date information provided by the clock circuit57 is written immediately to a buffer signifying the detection of awaveform capture event.

The voltage handler 230 also retrieves the circular buffer contents(step 390). In particular, as discussed above, the circular buffercontents include the previous MM cycles worth of waveform sample data.The voltage handler 230 generates a power quality event recordcomprising the circular buffer contents and the time and dateinformation.

The voltage handler 230 then writes the record to a memory and/orcommunicates the record to the utility customer or the utility generatoror supplier (step 395). As discussed above, it is often preferable toobtain several cycles of waveform sample data after the power qualityevent is identified in step 335. To this end, the voltage handler 230may execute a subprocess in which the requisite number of additionalline voltage samples are provided to the power quality event datarecord.

After step 395, the voltage handler 230 has determined that the linevoltage magnitude has returned to within normal parameters. The voltagehandler 230 than returns to step 305 of FIG. 7A and proceedsaccordingly. Referring again to step 355, if it is determined that thevariation of the present measure of VOLT is not below the firstvariation threshold, then the voltage handler 230 executes a sequence ofoperations that determine whether the variation of VOLT exceeds a secondvariation threshold, which could indicate a sub-event within thepresently detected power quality event.

In particular, if in step 355 it is determined that the variation ofVOLT is not below the first variation threshold, then the variationreduction duration index M is reset to zero (step 360). The voltagehandler 230 then determines whether the variation of VOLT from a valuerepresentative of the expected line voltage exceeds the second variationthreshold (step 405).

In particular, the second variation threshold corresponds to a secondpredetermined set point level that is in the same direction as the firstset point level. In other words, if the first variation threshold thatwas exceeded was a variation of the line voltage below the expectedvoltage level, then the second variation threshold is a variation of theline voltage further below the expected voltage level. Conversely, ifthe first variation threshold that was exceeded was a variation of theline voltage above the expected voltage level, then the second variationis a variation of the line voltage further above the expected linevoltage level.

If the variation is not greater than the second variation threshold,then the second variation duration counter L is reset to zero (step 415)and the voltage handler 230 returns to await further values of VOLT atstep 350.

If, however, the variation is greater than the second variationthreshold, then the voltage handler 230 increments the second variationduration index L (step 410). After the counter L is incremented, thevoltage handler 230 determines whether L exceeds a predetermined secondvariation duration value (step 420). The second variation duration valuerepresents a minimum number of half-cycles that the variation of VOLTmust exceed the second variation threshold to trigger the waveformcapture, which provides similar protections from spurious voltageanomalies as those discussed above in connection with step 325.

If the voltage handler 230 determines that L does not exceed thepredetermined second variation duration value, then the voltage handlerreturns to step 350 to receive the next voltage magnitude value andproceed accordingly.

If, however, L exceeds the second variation duration value, then thevoltage handler resets L (step 425) and obtains the time and dateinformation corresponding to the detection (step 430). The voltagehandler 230 also retrieves the circular buffer contents (step 435). Thevoltage handler 230 then generates a power quality event recordcomprising the circular buffer contents, the time and date information,and a predetermined number of post detection line voltage samples. Thevoltage handler 230 then writes the record to a memory and/orcommunicates the record to the utility customer or the utility generatoror supplier (step 440).

Thus, once power quality event has been detected in steps 305 to 325,the meter 40 of the present invention monitors for a second level ofvariation of the line voltage (or line current) from an expected value.Such a second level of variation may be preprogrammed as a second setpoint into the meter 40 by an operator as discussed below in connectionwith FIG. 9. As discussed above, the meter 40 then captures the waveformof the line voltage at the time surrounding the detection of the secondlevel of variation. Such information provides further, in depthinformation relating to a power quality event. Power providers,generators, and consumers may use such information to learn about howand why the event occurred, and what effect it may have had on the powerconsumer's equipment.

An exemplary use of the captured waveform data for two or more suchnested levels of variation within a disturbance event is to plot thedata in order to measure customer equipment response to the disturbanceas compared to standard power quality tolerance curves. One such powerquality disturbance curve is the Computer Business EquipmentManufacturing Association (CBEMA) curve, which is provided in I.E.E.E.standard 446.

Once the second variation power quality event record has been generatedand stored and/or communicated in step 440, the voltage handler 230 thenmonitors the line voltage to detect when the variation is reduced toless than the second variation threshold (or first variation threshold).To this end, the voltage handler 230 executes the flow diagramillustrated in FIG. 7C, beginning with step 445. It is noted that inaccordance with the flow diagram illustrated in FIG. 7C, the voltagehandler 230 will cause waveform capture if the variation of VOLT fallsbelow the second variation threshold and not the first variationthreshold for a predetermined number of half-cycles. However, thevoltage handler 230 also monitors whether the variation of VOLT from theexpected value falls below the first variation threshold.

In step 445, the voltage handler 230 receives a voltage magnitudeinformation value, VOLT, from the FIR smoothing circuit 216. The voltagehandler 230 then determines whether the variation of VOLT from anexpected value is less than the second variation threshold (step 450).If so, then the voltage handler 230 proceeds to step 455. If not,however, then the voltage handler 230 proceeds to step 460. In step 460,an index J, which represents the number of consecutive values of VOLTthat varied from the expected value in an amount less than the secondvariation threshold, is reset to zero. After step 460, the voltagehandler returns to step 445 to await the next value of VOLT.

In step 455, which is executed when the variation of VOLT does fallbelow the second variation threshold, the index J is incremented.

The voltage handler 230 then determines whether the variation of VOLTfrom an expected value is less than the first variation threshold (step465). If so, then the voltage handler 230 increments the counter M (step470) and then proceeds to step 480. If not, however, then the voltagehandler 230 resets the value of M (step 475) and then proceeds to step480. Steps 465 through 475 begin accumulation of the index M in theevent that the line voltage returns to a value that is less than thefirst variation threshold before the value of J reaches the secondvariation reduction duration value. In other words, before the value ofJ is sufficient to signify that the sub-event represented by the secondvariation threshold is over, the line voltage may have returned towithin its normal parameters. In such a case, the steps 465 through 475begin incrementing the counter M for use when the voltage handler 230returns to the flow diagram in FIG. 7B, as discussed further below.

The voltage handler 230 then determines whether J exceeds the secondvariation reduction duration value (step 480). In particular, similar tothe detection of the first variation in steps 310 to 325, the voltagehandler 230 only records a reduction in the variation of the linevoltage from the second variation threshold if there are a predeterminednumber of half-cycles in which the variation is below the secondvariation threshold.

If J does not exceed the second variation reduction duration value, thenthe voltage handler 230 returns to step 445 to await further linevoltage information. If, however, M exceeds the second variationreduction duration value, then the voltage handler 230 performs thewaveform capture operations described below in connection with steps 485through 500. Accordingly, the meter 40 of the present invention performswaveform capture not only at the beginning and end of a power qualityevent, such as described above in connection with steps 330 through 395,but also at the beginning and end of a power quality sub-event within apower quality event. To this end, the meter 40 performs waveform captureboth when a variation of the line voltage exceeds each of two variationthresholds and when the variation of the line voltage is reduced belowone or both of those variation thresholds.

In step 485, the voltage handler 230 resets J. The voltage handler 230then records the time and date of the power quality event (step 490). Inparticular, the time and date information provided by the clock circuit57 is written immediately to a buffer signifying the detection of thewaveform capture event.

The voltage handler 230 also retrieves the circular buffer contents(step 495). The voltage handler 230 generates a power quality eventrecord comprising the circular buffer contents, the time and dateinformation, and a predetermined number of post detection line voltagesamples.

The voltage handler 230 then writes the record to a memory and/orcommunicates the record to the utility customer or the utility generatoror supplier (step 500). After step 500, the voltage handler returns tostep 375 of FIG. 7B and proceeds accordingly to determine whether thevalue of VOLT has varied from the expected value less than the amount ofthe first variation threshold for enough cycles to indicate that theentire power quality event is over.

It will be appreciated that the use of two nested variation thresholds,as discussed above in connection with FIGS. 7A, 7B and 7C, is given byway of example only. Those of ordinary skill in the art may readilymodify the embodiment described herein to accommodate three or morenested variation thresholds corresponding to three or more user-definedset points.

As discussed above, the power quality event data records generated bythe voltage handler 230 are provided to memory within the meter or todata communication ports 41-44 as the measuring by the meter 40continues. This signal variation information provided by the voltagehandler 230 of the meter 40 which reflects the quality of power not onlyprovides competitive information for utility companies and customersthereof, but also provides troubleshooting information for utilitycompanies and customers in areas of power distribution such as through asecondary distribution system.

The meter 40 of the present invention may further include circuitry forperforming energy management functions. FIG. 8A shows a functional blockdiagram of an energy management controller 90 that may be incorporatedinto the meter 40 of FIG. 3.

In general, the revenue accuracy meter 40 receives a signal from atemperature controller or HVAC controller from a customer 60 into atransducer 91. A signal is responsively converted to an electricalsignal by the transducer 91 and compared to temperature, or other energysystem data, to desired predetermined settings 92. This data is thenanalyzed by an energy analyzer 95 preferably to analytical calculateoptimum desired settings based on power cost or billing data 94 and/orto perform various load curtailment functions. The analyzer 95 thenresponsively communicates to a power customer's energy system to adjusttemperature or other energy system settings 93 as illustrated. Blocks92, 94 and 95 may suitably be carried out by the microprocessor 48.

Because the revenue accuracy meter 40 preferably includes a powerquality circuit 200, the energy management controller 90 of the meter 40can advantageous include real time information to the power customer 60about the quality of power received and how this affects the customer'senergy usage and control capabilities. Additionally, this informationcan then be used to adjust billing calculations or projected energyusage costs related to the quantity of power used and/or the quality ofthe power supplied from the power generator 80. It will also beunderstood by those skilled in the art that such a meter 40 according tothe invention may also include information related to a third party orsame party power generator such as a large industrial company, i.e.,cogeneration.

The energy management controller 90 also preferably provides centralizeddata retrieval and management from the energy analyzer 95 responsive topredetermined command signals from a customer 60. These functionalcapabilities preferably include spreadsheet interface, basic reporting,record-keeping, overall system control, enhanced user interfaces, andother real-time access to energy utilization data for statisticalmanipulation and graphic presentation to the customer 60. Thesemanipulation capabilities preferably are software driven with computerprograms resident in a microprocessor or memory in communicationtherewith, and preferably include kilowatt load curves for day, week,and month, kilowatt duration curves, kVA/kQ load curves, power factorcurves, energy worksheets, demand worksheets, excessive reactiveworksheets, fuel recovery, contract minimum demand, rate worksheets,billing dates table, demand history table, season demand multipliertable, and predictive monitoring. The communication is preferablythrough a modem or other data communication interface, i.e., datacommunication ports 41-44, with the customer 60 as understood by thoseskilled in the art.

Also, according to the present invention as described above and asfurther illustrated in FIGS. 1-8, methods of measuring the quality ofpower received by a power customer 60 are provided. The method of thepresent invention preferably includes determining frequency and durationof undesired variations in an electrical signal representative of powerreceived by a power customer 60 across electrical power lines during aplurality of predetermined time periods and communicating a signalrepresentative of the undesired power variations to a power generator80. The method preferably further includes measuring power usage of apower customer 60 responsive to an electrical signal representative of acustomer load and communicating a signal representative of the amount ofpower used responsive to a command signal received from a powergenerator 80 or other entity.

Another method of measuring the quality of power supplied acrosselectrical power lines by a power generator 80 is further provided bythe present invention. The method preferably includes receiving ananalog signal representative of voltage received across electrical powerlines and converting the received analog signal to a digital signalrepresentative of the voltage. The frequency and duration of undesiredvariations in the digital voltage signal during a plurality ofpredetermined time periods are then determined. The data representativeof these undesired variations are then stored and signals representativeof the frequency and duration variations are transmitted to a powergenerator 80 responsive to a predetermined command signal received fromthe power generator 80. The step of determining frequency and durationof undesired variations preferably includes comparing a voltage signalto a predetermined voltage threshold value and determining a time periodthat the voltage signal is above or below the predetermined voltagethreshold value. Further, the methods preferably also includes measuringpower usage of a power customer responsive to an electrical signalrepresentative of a customer load, and communicating a signalrepresentative of the amount of power used responsive to a commandsignal received from a power generator. The power usage also may then becontrolled responsive to predetermined command signals received from apower customer.

By providing power quality and power usage measurement, as well as otherbeneficial functions such as energy management control 90, in a revenueaccuracy meter, the meter 40, and associated methods, of the presentinvention provides a compact and relatively inexpensive solution toproblems associated with prior devices and systems. Additionally, thedata communications capabilities of a revenue accuracy meter 40 of theinvention enhances a power generator's capability to monitor powerquality situations at specific customer sites, i.e., including problemsin the secondary power distribution system 36, remote from the powergenerating stations 21 or SCADA control facilities 22. These problems,for example, may include harmonic distortion, surges, sags, or otherdisturbances that greatly affect the quality of power received by thepower customer 60 at its industrial/commercial facility 41 or residence42.

FIG. 9 shows a block diagram of a control programmer 600 for use inconnection with the meter 40. In particular, the control programmer 600is a device that may be used to program control parameters into themeter 40. The control programmer 600 may be a stand alone, portableprogrammer or laptop computer that communicates through the optical portin the meter 40, or may be a remote computer that communicates throughone or more of the other communication ports 41, 42, 43, or 44.

The control programmer 600 includes a user interface 605 operable toreceive control parameters for the meter 40, including informationidentifying a first variation threshold and the second variationthreshold. To this end, the user interface 605 may suitably include akeypad or keyboard input device and a display for feedback.

The control parameters may further include metering calibration values,user defined configurations of reports obtained by the meter 40, andon/off controls for various meter features. The first and secondvariation thresholds may suitably be provided as first and second setpoints above the expected line voltage and first and second set pointsbelow the expected line voltage. Other power quality related parametersmay include the number of waveform cycles before and after an eventwhich are to be captured (timing parameters), the first and secondvariation duration values, the first and second variation reductionvalues, the number of events stored in non-volatile memory as opposed tovolatile memory.

Still other control parameters may define whether, when, how and whereto automatically communicate power quality event records. Suchparameters may be used to provide differing quantities of power qualityevent records to different external locations using differentcommunication methodologies. Accordingly, the meter 40 is preferablyconfigured to provide flexible captured waveform communicationcapabilities in addition to the above described advantages.

Coupled to or integral with the user interface 605 is a programmingdevice 610. The programming device 610 is a device that is configured toprovide information to the electrical meter 40. In particular, theprogramming device 610 is operable to communicate the control parametersidentified above to the electrical energy meter 40. To this end, theprogramming device 610 may suitably convert the control parameters inthe form obtained by the user interface 605 to a table of parametervalues in a form that is utilized by the meter 40.

The programming device 610 then communicates the control parametersthrough one of the communication ports 41, 42, 43, and 44. The table ofparameter values may suitably be stored in the meter 40 in thenon-volatile memory 53. The microprocessor 48 and/or DSP circuit 45 maythen download and/or retrieve the parameters as necessary.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of a revenue accuracy meter 40, and associatedmethods, according to the invention and, although specific terms areemployed, they are used in a descriptive sense only and not for purposesof limitation. The invention has been described in considerable detailwith specific reference to these various illustrated embodiments. Itwill be apparent, however, that various modifications and changes can bemade within the spirit and scope of the invention as described in theforegoing specification and as defined in the appended claims.

For example, while the above-described embodiments show a power qualitymeter in which multiple set points for waveform capture arepreprogrammed into the meter 40, waveform capture may also be, oralternatively be, triggered through receipt of an externally-generatedtrigger signal, such as one received through one of the communicationports 41, 42, 43, 44.

Moreover, it is noted that the source of externally-generated timestandard information could alternatively be a communication receiverthat is coupled to a time standard source within another meter. Forexample, if several meters are located on a local area network, it ispossible to have only one meter that includes a GPS, WWV OR IRIGreceiver and to have that meter communicate the calendar clockinformation to the other meters on the LAN periodically to calibrate allthe clocks.

Finally, while the exemplary embodiment described above focusesprimarily on handling detected line voltage variations, it may beadvantageous in some circumstances to provide the waveform capturefeatures of the present invention in connection with other line energyvariations, such as line current variations.

We claim:
 1. In an electrical energy meter containing means therein formetering a quantity of electrical energy generated by a supplier andtransferred via a power supply line to a load during an energymeasurement time interval, a method of monitoring variations in theelectrical energy, comprising the steps of: a) sensing a line voltagetransferred via the power supply line to the load during the energymeasurement time interval; b) detecting a variation in a magnitude ofthe sensed line voltage relative to an acceptable voltage level, whereinthe variation exceeds a first variation threshold; c) capturing a firstwaveform of the sensed line voltage corresponding to the time when saidvariation is detected; d) detecting a subsequent reduction in thevariation of the magnitude of the sensed line voltage such that thevariation is equal to or less than the first variation threshold; and e)capturing a second waveform of the sensed line voltage corresponding tothe time when the subsequent reduction in the variation is detected. 2.The method of claim 1 wherein step b) further comprises detecting avariation in a magnitude of the sensed line voltage relative to anacceptable voltage level wherein said variation comprises a decrease insaid sensed line voltage below the acceptable voltage level.
 3. Themethod of claim 1 wherein step b) further comprises detecting avariation in a magnitude of the sensed line voltage relative to anacceptable voltage level wherein said variation comprises an increase insaid sensed line voltage above the acceptable voltage level.
 4. Themethod of claim 1 wherein step c) further comprises capturing a firstwaveform by storing information representative of the first waveform ina memory.
 5. The method of claim 4 wherein step c) further comprisescapturing a first waveform by storing information representative of thefirst waveform in the memory wherein said memory comprises anon-volatile memory.
 6. The method of claim 1 further comprising thestep of communicating the captured first waveform and the capturedsecond waveform to the supplier.
 7. The method of claim 6, wherein saidcommunicating step comprises transferring data from a modem internal tothe meter to a telephone line operatively connected thereto via a dataport.
 8. The method of claim 1 further comprising the steps of:detecting a subsequent variation in a magnitude of the sensed linevoltage relative to an acceptable voltage level, wherein said variationexceeds the first variation threshold and a second variation threshold;and capturing a third waveform of the sensed line voltage correspondingto the time when said variation exceeding the first variation thresholdand the second variation threshold is detected.
 9. The method of claim 8further comprising the steps of: detecting a subsequent reduction in thevariation of the magnitude of the sensed line voltage such that thevariation is equal to or less than the second variation threshold andgreater than the first variation threshold; capturing a fourth waveformof the sensed line voltage corresponding to the time when the subsequentreduction in the variation is detected.
 10. The method of claim 1further comprising the step of obtaining user input identifying thefirst variation threshold.
 11. The method of claim 1 wherein step c)further comprises capturing the first waveform such that said capturedfirst waveform includes information representative of a the sensed linevoltage prior to and contemporaneous with the detection of saidvariation.
 12. The method of claim 1 wherein step c) further comprisescapturing the first waveform such that said captured first waveformincludes information representative of the sensed line voltagecontemporaneous with and subsequent to the detection of said variation.13. The method of claim 1 wherein step c) further comprises capturingthe first waveform such that said captured first waveform includesinformation representative of the sensed line voltage prior to,contemporaneous with, and subsequent to the detection of said variation.14. An electrical energy meter for detecting line voltage variations inreal-time, comprising: a voltage digitizing circuit operable to obtainanalog line voltage information and generate digital line voltageinformation therefrom; a current digitizing circuit operable to obtainanalog line current information and generate digital line currentinformation therefrom; a metering circuit operable to receive thedigital line voltage information and the digital line currentinformation and generate metering information therefrom; a power qualitycircuit operable to receive the digital line voltage information andobtain magnitude information therefrom, the magnitude informationrepresentative of the magnitude of the line voltage, detect a variationin the magnitude of the line voltage relative to an acceptable voltagelevel, wherein said variation exceeds a first variation threshold,capture a first waveform in the form of a first set of digital linevoltage information corresponding to the time when said variation isdetected, detect a subsequent reduction in the variation of themagnitude of the line voltage such that the variation is equal to orless than the first variation threshold, capture a second waveform inthe form of a second set of digital line voltage informationcorresponding to the time when the subsequent reduction in the variationis detected.
 15. The electrical energy meter of claim 14 wherein thepower quality circuit is further operable to detect a variation in amagnitude of the line voltage relative to an acceptable voltage levelwherein said variation comprises a decrease in said line voltage belowthe acceptable voltage level.
 16. The electrical energy meter of claim14 wherein the power quality circuit is further operable to detect avariation in a magnitude of the line voltage relative to an acceptablevoltage level wherein said variation comprises an increase in saidsensed line voltage above the acceptable voltage level.
 17. Theelectrical energy meter of claim 14 wherein the power quality circuitincludes at least one memory for capturing the first waveform in theform of digital line voltage information corresponding to the time whensaid variation is detected.
 18. The electrical energy meter of claim 17wherein the at least one memory includes at least one non-volatilememory.
 19. The electrical energy meter of claim 14 further comprising acommunication circuit, the communication circuit connected to the powerquality circuit and operable to communicate the captured first waveformand the captured second waveform to the supplier.
 20. The electricalenergy meter of claim 19 wherein said communication circuit includes amodem that is operably connected to a telephone line via a data port.21. The electrical energy meter of claim 14 wherein the power qualitycircuit is further operable to: detect a variation in a magnitude of theline voltage relative to an acceptable voltage level, wherein saidvariation exceeds the first variation threshold and a second variationthreshold; and capture a third waveform in the form of a first set ofdigital line voltage information corresponding to the time when saidvariation that exceeds the first variation threshold and the secondvariation threshold is detected.
 22. The electrical energy meter ofclaim 21 wherein the power quality circuit is further operable to:detect a subsequent reduction in the variation of the magnitude of theline voltage such that the variation is equal to or less than the secondvariation threshold and greater than the first variation threshold; andcapture a fourth waveform in the form of a first set of digital linevoltage information corresponding to the time when the subsequentreduction in the variation is detected.
 23. An apparatus for providingcontrol parameters to an electrical energy meter, the electrical energymeter having a power quality circuit, the power quality circuit operableto capture a first waveform of a sensed line voltage corresponding to atime when a variation of the sensed line voltage relative to anacceptable voltage level exceeds a first variation threshold, andfurther operable to capture a second waveform of a sensed line voltagewhen the variation of the sensed line voltage relative to an acceptablevoltage level exceeds a second variation threshold, the apparatuscomprising: a) a user interface operable to receive informationidentifying a first variation threshold and the second variationthreshold; b) a programming device configured to provide information tothe electrical meter, the programming device operable to communicatecontrol parameters to the electrical energy meter, the controlparameters including the information identifying the first variationthreshold and the second variation threshold.
 24. The apparatus of claim23 wherein the user interface is further operable to receive informationidentifying timing parameters of the first captured waveform and thesecond captured waveform.
 25. In an electrical energy meter containingmeans therein for metering a quantity of electrical energy generated bya supplier and transferred via a power supply line to a load of acustomer during an energy measurement time interval, a method ofmonitoring variations in the metered quantity of electrical energy,comprising the steps of: a) sensing a line voltage transferred via thepower supply line to the load during the energy measurement timeinterval; b) detecting a variation in a magnitude of the sensed linevoltage relative to an acceptable voltage level, wherein said variationexceeds a first variation threshold; c) capturing a first waveform ofthe sensed line voltage corresponding to the time when said variation isdetected; d) detecting a subsequent variation in the magnitude of thesensed line voltage relative to the acceptable voltage level, whereinsaid subsequent variation exceeds a second variation threshold; and e)capturing a second waveform of the sensed line voltage corresponding tothe time when the subsequent variation is detected wherein thesubsequent variation exceeds the acceptable voltage level when thevariation exceeds the acceptable voltage level, and the subsequentvariation is less than the acceptable voltage level when the variationis less than the acceptable voltage level.
 26. The method of claim 25wherein step b) further comprises detecting a variation in a magnitudeof the sensed line voltage relative to an acceptable voltage levelwherein said variation comprises a decrease in said sensed line voltagebelow the acceptable voltage level.
 27. The method of claim 25 whereinstep b) further comprises detecting a variation in a magnitude of thesensed line voltage relative to an acceptable voltage level wherein saidvariation comprises an increase in said sensed line voltage above theacceptable voltage level.
 28. The method of claim 25 wherein step c)further comprises capturing a first waveform by storing informationrepresentative of the first waveform in a memory.
 29. The method ofclaim 25 wherein step c) further comprises capturing a first waveform bystoring information representative of the first waveform in the memorywherein the memory comprises a non-volatile memory.
 30. The method ofclaim 25 further comprising the step of communicating the captured firstwaveform and the captured second waveform to the supplier.
 31. Themethod of claim 30, wherein said communicating step comprisestransferring data from a modem internal to the meter to a telephone lineoperatively connected thereto via a data port.
 32. The method of claim25 further comprising the step of obtaining user input identifying thefirst variation threshold and the second variation threshold.
 33. Themethod of claim 25 wherein step c) further comprises capturing the firstwaveform such that said captured first waveform includes informationrepresentative of a the sensed line voltage prior to and contemporaneouswith the detection of said variation.
 34. The method of claim 25 whereinstep c) further comprises capturing the first waveform such that saidcaptured first waveform includes information representative of thesensed line voltage contemporaneous with and subsequent to the detectionof said variation.
 35. The method of claim 25 wherein step c) furthercomprises capturing the first waveform such that said captured firstwaveform includes information representative of the sensed line voltageprior to, contemporaneous with, and subsequent to the detection of saidvariation.
 36. An electrical energy meter for detecting line voltagevariation in real-time, comprising: a voltage digitizing circuitoperable to obtain analog line voltage information and generated digitalline voltage information therefrom; a current digitizing circuitoperable to obtain analog line current information and generate digitalline current information therefrom; a metering circuit operable toreceive the digital line voltage information and the digital linecurrent information and generate metering information therefrom; a powerquality circuit operable to receive the digital line voltage informationand obtain magnitude information therefrom, the magnitude informationrepresentative of the magnitude of the line voltage, detect a variationin the magnitude of the line voltage relative to an acceptable voltagelevel, wherein said variation exceeds a first variation threshold,capture a first waveform in the form of a first set of digital linevoltage information corresponding to the time when said variation isdetected, detect a subsequent variation of the magnitude of the linevoltage, wherein said subsequent variation exceeds a second variationthreshold, and capture a second waveform in the form of a second set ofdigital line voltage information corresponding to the time when thesubsequent variation is detected wherein the subsequent variationexceeds the acceptable voltage level when the variation exceeds theacceptable voltage level, and the subsequent variation is less than theacceptable voltage level when the variation is less than the acceptablevoltage level.
 37. The electrical energy meter of claim 36 wherein thepower quality circuit is further operable to detect a variation in amagnitude of the line voltage relative to an acceptable voltage levelwherein said variation comprises a decrease in said line voltage belowthe accept able voltage level.
 38. The electrical energy meter of claim36 wherein the power quality circuit is further operable to detect avariation in a magnitude of the line voltage relative to an acceptablevoltage level wherein said variation comprises an increase in saidsensed line voltage above the acceptable voltage level.
 39. Theelectrical energy meter of claim 36 wherein the power quality circuitincludes at least one memory for capturing the first waveform in theform of digital line voltage information corresponding to the time whensaid variation is detected.
 40. The electrical energy meter of claim 36wherein the power quality circuit includes at least one non-volatilememory for capturing the first waveform in the form of digital linevoltage information corresponding to the time when said variation isdetected.
 41. The electrical energy meter of claim 36 further comprisinga communication circuit, the communication circuit connected to thepower quality circuit and operable to communicate the captured firstwaveform and the captured second waveform to the supplier.
 42. Theelectrical energy meter of claim 41 wherein said communication circuitincludes a modem internal that is operably connected to a telephone linevia a data port.
 43. In an electrical energy meter containing meanstherein for metering a quantity of electrical energy generated by asupplier and transferred via a power supply line to a load during anenergy measurement time interval, a method of monitoring variations inthe electrical energy, comprising the steps of: a) sensing a line energysignal transferred via the power supply line to the load during theenergy measurement time interval; b) detecting a variation in amagnitude of the sensed line energy signal relative to an acceptableline energy level, wherein the variation exceeds a first variationthreshold; c) capturing a first waveform of the sensed line energysignal corresponding to the time when said variation is detected; d)detecting a subsequent reduction in the variation of the magnitude ofthe sensed line energy signal such that the variation is equal to orless than the first variation threshold; and e) capturing a secondwaveform of the sensed line energy signal corresponding to the time whenthe subsequent reduction in the variation is detected.
 44. The method ofclaim 43 wherein said line energy signal comprises a line current.